WO2015197361A1

WO2015197361A1 - Piston ring

Info

Publication number: WO2015197361A1
Application number: PCT/EP2015/062904
Authority: WO
Inventors: Richard Mittler; Jörn Pröpper
Original assignee: Federal-Mogul Burscheid Gmbh
Priority date: 2014-06-26
Filing date: 2015-06-10
Publication date: 2015-12-30
Also published as: US10125870B2; US20170130840A1; DE102014108973A1; CN106103960A; EP3161355B1; PT3161355T; EP3161355A1; CN106103960B

Abstract

The invention relates to a piston ring for a piston of a piston engine, comprising an outside peripheral surface (2), an inside peripheral surface (4), an upper flank (6) facing in the direction of the piston top side, and a lower flank (8) facing in the direction of the piston bottom side, wherein the lower flank (8) extends at an angle in relation to the upper flank (6), and therefore the axial height (A) of the piston ring on the outside peripheral surface (2) is greater than the axial height (B) on the inside peripheral surface (4), and wherein at least one recess (10) is provided in the upper flank (6) on each side of the joint of the piston ring.

Description

piston ring

The present invention relates to a piston ring with improved wear, wear and Ölab streif behavior. More particularly, the invention relates to a piston ring adapted to compensate for piston groove tilting which occurs during operation of a piston engine.

The piston of an internal combustion engine deforms during operation under the influence of combustion s heat and the resulting temperature distribution in the axial direction different. The highest temperatures prevail on the combustion chamber side, while the temperature decreases in the direction of the crankcase. The consequence of this is a tilting of the piston ring grooves, so that the flanks of the piston ring groove have a gradient with respect to the cylinder axis.

The piston ring located in the piston ring groove lies with its lower flank under the influence of the combustion pressure over the entire surface of the lower flank of the piston groove and therefore assumes with its cross section the same inclination as the groove. As a result, the pivot point of the piston ring tread shifts upward and thus changes the hydrodynamic properties, accompanied by an altered wear / wear behavior towards the upper running edge, increased oil film thicknesses and poorer oil streak behavior.

A known solution to this problem is to manufacture the groove flanks of the piston with a corresponding slope, which compensates for this effect, so that in operation under the influence of temperature, the groove flanks are perpendicular to the cylinder bore. In other words, the piston ring grooves are not formed with a rectangular cross-section with vertical to the cylinder barrel flanks, but with a trapezoidal Cross section with flanks oblique to the cylinder bore (each in the thermally undeformed state). However, this is compared to piston ring grooves with conventional rectangular cross-section associated with an increased manufacturing cost in the production of the piston and therefore disadvantageous.

The object of the present invention is therefore to provide a piston ring which compensates for the effect of Nutverkippung in a piston with conventional grooves of rectangular cross-section. This is cheaper and easier to implement than the known solution adapted piston ring grooves, as well as motors with conventional pistons can also be retrofitted with improved piston rings.

According to one aspect of the invention, there is provided a piston ring for a piston of a reciprocating engine comprising:

an outside peripheral surface;

an inside peripheral surface;

an upper flank pointing in the direction of the piston top side; and

a lower flank pointing in the direction of the piston underside;

in which

the lower flank extends obliquely with respect to the upper flank so that the axial height of the piston ring on the outer circumferential surface is greater than on the inner peripheral surface; and

wherein at least one recess in the upper flank is provided on each side of the joint of the piston ring.

To counteract the effect of Nutkippung, a piston ring is proposed with compensation of Kolbennutkippung. For this purpose, the ring is provided at its outer diameter with a larger axial height, while the height at the inner diameter receives the nominal height. The increased axial height at the outer diameter is to be chosen so that the lower edge of the ring receives the same slope as the groove during operation of the engine. As a result of the increased on the outer peripheral surface height, the axial clearance and the distance between the ring and groove is reduced there. This entails a reduced gas flow at this point and thus a reduced pressure build-up on the upper flank and the inside peripheral surface. This is disadvantageous since the piston ring is thus no longer optimally pressed against the cylinder wall or bushing in the particularly critical impact area and the gas-tightness therefore decreases. Among other things, this leads to increased blow-by losses.

This is inventively compensated by the fact that in the upper edge of the ring at least at the periphery in the region of the butt ends at least one recess, e.g. in the form of a trough, is introduced. As a result, the distance between the upper flank of the piston ring and the upper groove flank is deliberately increased or approximated to the value that would be present in a conventional piston ring. As a result, the gas flow is increased, so that the piston ring is pressed again in the desired manner to the cylinder wall or - liner.

According to one embodiment, the recesses extend into the outside peripheral surface. The recess according to the invention may be arranged only in the upper flank or extend into the outer circumferential surface.

According to one embodiment, a plurality of spaced-apart recesses are provided on each side of the joint.

In order to influence the gas flow in the desired manner, further recesses of the same shape can be introduced at certain intervals in the upper flank.

According to one embodiment, the recesses are arranged in a range of 0-90 ° on both sides of the joint. According to one embodiment, the distance of the recesses from the inside circumferential surface is at least 1/3 of the radial length of the upper flank. Or in other words, the recesses extend over a maximum of 2/3 of the radial wall thickness of the outer peripheral surface.

According to one embodiment, the upper flank forms a right angle with the inside circumferential surface.

According to one embodiment, the bevel of the lower flank is adapted to compensate for the tilting of the corresponding piston groove of the piston during operation of the piston engine.

Preferably, the slope of the lower edge of the piston ring is designed so that it is substantially compensated for in the groove tilt occurring during operation.

Preferably, the dimensions of axial depth and / or radial width and / or tangential length of the recesses depend on the distance to the annular joint and / or from the radial distance from the inside of the piston ring. Alternatively or additionally, it is preferred that the number and / or the distances of the recesses depend on the distance to the ring impact and / or on the radial distance from the inside of the piston ring.

Brief description of the figures

Fig. 1 is a cross-sectional view of a conventional piston ring in a tilted annular groove;

FIG. 2 is a cross-sectional view of a piston ring with a lower flank tapered according to the invention; FIG. Fig. 3 is a cross-sectional view of a piston ring of Fig. 2 in an untilted annular groove; FIG. 4 is a cross-sectional view of the piston ring of FIG. 3 in the tilted annular groove; FIG.

5 is a cross-sectional view of a piston ring according to one embodiment in an untilted annular groove;

Fig. 6 is a cross-sectional view of a piston ring according to another embodiment in an untilted annular groove;

Fig. 7 is a cross-sectional view of a piston ring according to another embodiment in an untilted annular groove;

Fig. 8 is a three-dimensional cross-sectional view of a piston ring according to the embodiment of Fig. 6; and FIG. 9 shows, in a plan view of an embodiment of a piston ring, the angular distribution of the recesses with respect to the ring impact.

Detailed Description In Fig. 1, a conventional piston ring is shown with parallel rectangular flanks. The situation with not tilted piston ring groove is shown in dashed lines. In the cold state of the engine in question, the geometry of the piston ring groove is rectangular. Due to the different thermal loads in the axial direction during operation of the motor (high thermal load on the piston crown, lower thermal load in the direction of the cylinder block), different thermally induced deformations occur. This tilts the annular groove in the manner shown by solid lines (not necessarily true to scale).

In engine operation occurs by the gas pressures occurring during combustion gas on the upper edge 6 of the piston ring over in the space between the annular groove and the piston ring. As a result, the piston ring is pressed in a desired manner downwards and outwards to seal against the cylinder wall or liner. The also executed with a rectangular geometry conventional piston ring sets by this effect with its lower edge 8 over the entire surface of the lower edge of the piston ring groove. Since the piston ring is tilted by the thermal influences and thus the lower edge is inclined, this causes a rotation of the piston ring in relation to the situation with a cold engine.

The pivot point of the piston ring, i. the contact point of the crowned running surface with the cylinder wall runner, thereby migrated upward compared to the undeformed state. This leads to a deterioration of the hydrodynamic properties, the load and wear behavior is shifted or increased in the direction of the upper edge 6 of the piston ring. There are larger oil film thicknesses and by the associated with the rotation greater distance of the lower edge of the cylinder wall or liner on a deteriorated Ölabstreifverhalten.

According to the invention, this is remedied by providing a piston ring with an oblique lower flank 8. The ring has a greater axial height A on the outer circumferential surface than the axial height B on the inner circumferential surface. The enlarged axial height A on the outer peripheral surface is to be chosen so that the lower annular edge 8 receives the same slope as the annular groove in the tilted state. Such a piston ring is shown in Fig. 2 in cross section.

This ensures that the piston ring rests as intended on the cylinder wall or liner during engine operation. The above-mentioned effects, which deteriorate the efficiency of the engine, are thereby prevented.

However, this changed geometry leads to the fact that on the outer circumferential surface 2, the axial play between the annular groove and the piston ring is reduced compared to the conventional rectangular piston ring or the play on the inner peripheral surface 4 (i <h ₂ ), as shown in FIGS (untilted ring groove) and 4 (tilted ring groove) can be seen. This results in a reduced gas flow and thus the pressure at the upper flank 6 and the inside peripheral surface 4 of the piston ring reduced. The desired effect of application under combustion pressure to the cylinder wall or liner is also reduced, which leads to greater distance from the cylinder wall or liner. This in turn can follow larger oil film thicknesses, reduced tightness and deteriorated Ölab streaking behavior. This occurs in particular in the area of the ring impact.

According to the invention is therefore further proposed to provide on each side of the joint of the piston ring at least one recess 10 in the upper ring edge. Through the recess 10, the game or the distance between the upper edge of the annular groove and the upper edge 6 of the piston ring is increased locally. As a result, the gas flow is increased, so that the piston ring can be pressed again in the desired manner from the combustion pressure to the cylinder wall or liner. Various exemplary embodiments are shown in Figs. 5-7. Fig. 5 shows a variant in which the recess 10 is made substantially half round. The recess is located only in the upper flank 6 of the piston ring, i. it does not protrude into the tread 2. In the preferred embodiment shown here, the recess 10 is arranged such that it lies substantially centrally below the upper edge of the annular groove. This variant is particularly suitable for piston rings with a sufficiently large projection over the annular groove. It is advantageous here that the tread 2 remains untouched.

In general, in order to counteract the throttling of the gas flow, the recess (s) in the region of the narrowest point between groove and ring should already have a certain depth in the axial direction (n). The goal is to increase the cross section perpendicular to the gas flow direction.

Fig. 6 shows a variant in which the recess 10 also partially protrudes into the tread 2 of the piston ring. This variant is particularly suitable for piston rings, which protrude only relatively little beyond the groove. By protrude into the tread 2 is still a sufficient distance from the annular groove and thus sufficient space for the Gas passage created. The disadvantage here may be that the surface of the tread 2 is reduced at least locally.

Fig. 7 shows a further variant in which in this case three recesses 10 are arranged one behind the other in the radial direction. This serves to reinforce the gas passage. The shape, depth, number and the distances of recesses 10 in both the radial and tangential direction are variable and can be made flexible. For example, the axial depth of the recesses may be designed to be decreasing in radial direction one after the other in the direction of the ring inner side (not shown).

Fig. 8 shows an embodiment according to which the recesses 10 are provided both in the tread 2 and the upper flank 6 of the piston ring, wherein the radial dimension is selected so that it is at most 2/3 of the radial width of the piston ring. As can also be seen here, in this embodiment, the depth and also the tangential width of the recesses 10 decrease towards the inside circumferential surface of the piston ring.

By varying the parameters "dimensions" and "distances" of the recesses, the contact pressure can be flexibly adjusted by the combustion, for example as a function of the distance from the ring impact, depending on the local preload etc. This can be achieved by providing more (on the one hand). in the radial direction) recesses occur at locations that are closer to the impact, or by smaller distances of the recesses toward the shock out, or by appropriate choice of a larger axial depth / radial width / tangential length depending on the distance to the ring impact. Another possible alternative is a single in the tangential direction long recess per side of the ring impact, which then varies in their dimensions "axial depth" / "radial width" / "tangential length" so that, depending on the distance to the ring impact of the contact pressure The butt ends differ from the opposite ring back by a poorer adaptability to the cylinder curvature, since the piston ring to the The radial pressure distribution is thus dependent on the position on the piston ring in relation to the butt ends or the ring back, respectively, since it is thus primarily necessary on the ring impact to achieve an improved engagement of the piston ring. It is sufficient, according to the invention, to provide the recesses in the abutting area in order to reinforce the abutment by the combustion pressure .Figure 9 shows an exemplary arrangement in which the recesses are arranged at intervals from one another and up to a maximum of 90 ° from the annular abutment the arrangement and dimensioning of the recesses are selected depending on the radial pressure distribution of the piston ring so that the same contact pressure on the cylinder wall or bush is obtained in engine operation at all points of the piston ring as possible.

Unless explicitly described otherwise, in principle all individual features of the described exemplary embodiments can be combined with one another as desired.

Claims

claims

Piston ring for a piston of a reciprocating engine, comprising:

an outside peripheral surface (2);

an inside peripheral surface (4);

an upper flank (6) pointing in the direction of the piston top side; and a lower flank (8) facing towards the lower side of the piston;

in which

the lower flank (8) slopes relative to the upper flank (6) so that the axial height (A) of the piston ring on the outer peripheral surface (2) is greater than the axial height (B) on the inner peripheral surface (4); and wherein on each side of the joint of the piston ring at least one recess (10) in the upper flank (6) is provided.

Piston ring according to claim 1,

wherein the recesses (10) extend into the outer peripheral surface (2).

Piston ring according to claim 1 or 2,

wherein a plurality of spaced-apart recesses (10) are provided on each side of the joint.

Piston ring according to one of the preceding claims,

wherein the recesses (10) are arranged in a range of 0-90 ° on both sides of the joint.

Piston ring according to one of the preceding claims,

wherein the distance of the recesses (10) from the inside peripheral surface is at least 1/3 of the radial length of the upper flank (6).

Piston ring according to one of the preceding claims, wherein the upper flank (6) forms a right angle with the inside peripheral surface (4).

Piston ring according to one of the preceding claims, wherein the chamfer of the lower edge (8) is adapted to compensate for the tilting of the corresponding piston groove of the piston during operation of the piston engine.

Piston ring according to one of the preceding claims, wherein the dimensions axial depth and / or radial width and / or tangential length of the recesses (10) depend on the distance to the ring impact and / or the radial distance from the inside of the piston ring.

Piston ring according to one of the preceding claims, wherein the number and / or the distances of the recesses (10) depend on the distance to the annular joint and / or the radial distance from the inside of the piston ring.